Longitudinal measurement of subcutaneous and intratibial human prostate cancer xenograft growth and response to ionizing radiation by plasma Alu and LINE-1 ctDNA: A comparison to standard methods.

BACKGROUND: Current preclinical models of metastatic prostate cancer (PCa) require sophisticated technologies and/or genetically engineered cells for the noninvasive monitoring of tumors in remote sites, such as bone. Recent developments in circulating tumor DNA (ctDNA) analysis provide an alternative method for noninvasive tumor monitoring at a low cost. Here, we sought to evaluate human Alu and LINE-1 ctDNA for the longitudinal measurement of subcutaneous and intratibial human PCa xenograft growth and response to ionizing radiation (IR) through comparison with standard slide caliper and bioluminescence measurements. MATERIAL AND METHODS: Intratibial and subcutaneous xenografts were established in male athymic nude mice using LNCaP cells that stably express firefly luciferase. A subset of tumors was treated with a single dose of IR (CT-guided focal IR, 6 Gy). Tumor measurements were simultaneously taken by slide caliper (subcutaneous only), in vivo bioluminescence imaging, and quantitative real-time PCR (qPCR) of human-specific Alu and LINE-1 ctDNA for several weeks. RESULTS: Levels of ctDNA and bioluminescence increased concordantly with subcutaneous and intratibial tumor growth. A statistically significant correlation (Spearman) was observed between ctDNA and subcutaneous tumor volume (LINE-1, r = .94 and Alu, r = .95, p < .0001), ctDNA and bioluminescence (LINE-1, r = .66 and Alu, r = .60, p < .002), and bioluminescence and tumor volume (r = .66, p = .0003). Bioluminescence and ctDNA were also significantly correlated in intratibial tumors (LINE-1, r = .82 and Alu, r = .81, p < .0001). Following external beam IR, the tumor responses varied briefly by method of measurement, but followed a similar trend. Statistically significant correlations were maintained between ctDNA and slide caliper measurement in irradiated subcutaneous tumors (LINE-1, r = .64 and Alu, r = .44, p < .02), and ctDNA and bioluminescence in intratibial tumors (LINE-1, r = .55, p = .018). CONCLUSIONS: Real-time qPCR of circulating human Alu and LINE-1 DNA provides an accurate measurement of subcutaneous and intratibial xenograft burden that is comparable with conventional bioluminescence imaging and slide caliper measurement. Transient differences in measurements were observed following tumor-targeted IR, but overall all measurements mirrored tumor growth and response.

Cellular Delivery of Bioorthogonal Pretargeting Therapeutics in PSMA-Positive Prostate Cancer.

Prostate cancer is primarily fatal after it becomes metastatic and castration-resistant despite novel combined hormonal and chemotherapeutic regimens. Hence, new therapeutic concepts and drug delivery strategies are urgently needed for the eradication of this devastating disease. Here we report the highly specific, in situ click chemistry driven pretargeted delivery of cytotoxic drug carriers to PSMA(+) prostate cancer cells. Anti-PSMA 5D3 mAb and its F(ab')2 fragments were functionalized with trans-cyclooctene (TCO), labeled with a fluorophore, and used as pretargeting components. Human serum albumin (ALB) was loaded with the DM1 antitubulin agent, functionalized with PEGylated tetrazine (PEG4-Tz), labeled with a fluorophore, and used as the drug delivery component. The internalization kinetics of components and the therapeutic efficacy of the pretargeted click therapy were studied in PSMA(+) PC3-PIP and PSMA(-) PC3-Flu control cells. The F(ab')2 fragments were internalized faster than 5D3 mAb in PSMA(+) PC3-PIP cells. In the two-component pretargeted imaging study, both components were colocalized in a perinuclear location of the cytoplasm of PC3-PIP cells. Better colocalization was achieved when 5D3 mAb was used as the pretargeting component. Consecutively, the in vitro cell viability study shows a significantly higher therapeutic effect of click therapy in PC3-PIP cells when 5D3 mAb was used for pretargeting, compared to its F(ab')2 derivative. 5D3 mAb has a longer lifetime on the cell surface, when compared to its F(ab')2 analogue, enabling efficient cross-linking with the drug delivery component and increased efficacy. Pretargeting and drug delivery components were cross-linked via multiple bioorthogonal click chemistry reactions on the surface of PSMA(+) PC cells forming nanoclusters, which undergo fast cellular internalization and intracellular transport to perinuclear locations.

Development of 5D3-DM1: A Novel Anti-Prostate-Specific Membrane Antigen Antibody-Drug Conjugate for PSMA-Positive Prostate Cancer Therapy.

Prostate cancer (PC) is a potentially high-risk disease and the most common cancer in American men. It is a leading cause of cancer-related deaths in men in the US, second only to lung and bronchus cancer. Advanced and metastatic PC is initially treated with androgen deprivation therapy (ADT), but nearly all cases eventually progress to castrate-resistant prostate cancer (CRPC). CRPC is incurable in the metastatic stage but can be slowed by some conventional chemotherapeutics and second-generation ADT, such as enzalutamide and abiraterone. Therefore, novel therapeutic strategies are urgently needed. Prostate-specific membrane antigen (PSMA) is overexpressed in almost all aggressive PCs. PSMA is widely used as a target for PC imaging and drug delivery. Anti-PSMA monoclonal antibodies (mAbs) have been developed as bioligands for diagnostic imaging and targeted PC therapy. However, these mAbs are successfully used in PC imaging and only a few have gone beyond phase-I for targeted therapy. The 5D3 mAb is a novel, high-affinity, and fast-internalizing anti-PSMA antibody. Importantly, 5D3 mAb demonstrates a unique pattern of cellular localization to the centrosome after internalization in PSMA(+) PC3-PIP cells. These characteristics make 5D3 mAb an ideal bioligand to deliver tubulin inhibitors, such as mertansine, to the cell centrosome, leading to mitotic arrest and elimination of dividing PC cells. We have successfully developed a 5D3 mAb- and mertansine (DM1)-based antibody-drug conjugate (ADC) and evaluated it in vitro for binding affinity, internalization, and cytotoxicity. The in vivo therapeutic efficacy of 5D3-DM1 ADC was evaluated in PSMA(+) PC3-PIP and PSMA(-) PC3-Flu mouse models of human PC. This therapeutic study has revealed that this new anti-PSMA ADC can successfully control the growth of PSMA(+) tumors without inducing systemic toxicity.

Adding the Team into T1 Translational Research: A Case Study of Multidisciplinary Team Science in the Evaluation of Biomarkers of Prostate Cancer Risk and Prognosis.

BACKGROUND: Given translational research challenges, multidisciplinary team science is promoted to increase the likelihood of moving from discovery to health effect. We present a case study documenting the utility of multidisciplinary team science in prostate cancer tissue biomarker validation. METHODS: We used primary data generated by a team consisting of a pathologist, cancer biologists, a biostatistician, and epidemiologists. We examined their contributions by phase of biomarker evaluation to identify when, through the practice of team science, threats to internal validity were recognized and solved. Next, we quantified the extent of bias avoided in evaluating the association of Ki67 (immunohistochemistry), stromal cell telomere length (fluorescence in situ hybridization), and microRNA (miRNA) (miR-21, miR-141, miR-221; quantitative RT-PCR) with prostate cancer risk or recurrence in nested case-control studies. RESULTS: Threats to validity were tissue storage time (Ki67, miRNA) and laboratory equipment maintenance (telomeres). Solutions were all in the data analysis phase and involved using tissue storage-time specific cutpoints and/or batch-specific cutpoints. Bias in the regression coefficient for quantiles of each biomarker ranged from 24% to 423%, and the coefficient for the test for trend ranged from 15% to 910%. The interpretation of the associations changed as follows: Ki67, null to positive; stromal cell telomere length, null to positive; miR-21 and miR-141 remained null; miR-221, weak to moderate inverse. CONCLUSIONS: In this case study, we documented the inferential benefits of multidisciplinary team science when the team's collaboration and coordination led to the identification of threats to validity and the implementation of appropriate solutions.

The orally active pterocarpanquinone LQB-118 exhibits cytotoxicity in prostate cancer cell and tumor models through cellular redox stress.

BACKGROUND: The targeted induction of reactive oxygen species (ROS) is a developing mechanism for cancer therapy. LQB-118 is a pterocarpanquinone and ROS-inducing agent with proven antineoplastic activity. Here, LQB-118 efficacy and mechanism of activity, were examined in Prostate Cancer (PCa) cell and tumor models. METHODS: PC3, LNCaP, and LAPC4 PCa cells were applied. Dicoumarol treatment was used to inhibit quinone reductase activity. N-acetylcysteine (NAC) was applied as a ROS scavenger. ROS production was quantified by H2 DCFDA flow cytometry. LQB-118 treated cells were evaluated for changes in lipid peroxidation, viability, and apoptosis. Treatment-induced gene expression was measured by RT-qPCR and Western Blot. SOD1 knockdown was achieved with siRNA or miRNA mimic transfection. MicroRNA specificity was determined by 3'UTR reporter assay. Oral LQB-118 treatment (10 mg/kg/day) efficacy was determined in athymic male nude mice bearing subcutaneous PC3 xenograft tumors. RESULTS: LQB-118 treatment triggered PCa cell death and apoptosis. Therapeutic activity was at least partially dependent upon quinone reduction and ROS generation. LQB-118 treatment caused an increase in cellular ROS and lipid peroxidation. Treated cells exhibited elevated levels of NQO1, Nrf2, and SOD1. The miRNAs miR-206, miR-1, and miR-101 targeted and reduced SOD1 expression. The knockdown of SOD1, by siRNA or miRNA, enhanced LQB-118 cytotoxicity. Orally administered LQB-118 treatment significantly reduced the growth of established PCa xenograft tumors. CONCLUSION: LQB-118 is a developing and orally active pterocarpanquinone agent that effectively kills PCa cells through quinone reduction and ROS generation. The inhibition SOD1 expression enhances LQB-118 activity, presumably by impairing the cellular antioxidant response.

Differential long-term stability of microRNAs and RNU6B snRNA in 12-20 year old archived formalin-fixed paraffin-embedded specimens.

BACKGROUND: The quantitative analysis of microRNA (miRNA) gene expression in archived formalin-fixed, paraffin embedded (FFPE) tissues has been instrumental to identifying their potential roles in cancer biology, diagnosis, and prognosis. However, it remains unclear whether miRNAs remain stable in FFPE tissues stored for long periods of time. METHODS: Here we report Taqman real-time RT-PCR quantification of miR-21, miR-141, miR-221, and RNU6B small nuclear RNA (snRNA) levels from 92 radical prostatectomy specimens stored for 12-20 years in FFPE blocks. The relative stability of each transcript over time was assessed using general linear models. The correlation between transcript quantities, sample age, and RNA integrity number (RIN) were determined utilizing Spearman rank correlation. RESULTS: All transcript levels linearly decreased with sample age, demonstrating a clear loss of miRNA stability and RNU6B snRNA stability over time. The most rapid rates of degradation were observed for RNU6B and miR-21, while miR-141 and miR-221 were more stable. RNA quality was not correlated with sample age or with miR-21, miR-221, or RNU6B snRNA levels. Conversely, miR-141 levels increased with RNA quality. CONCLUSIONS: MiRNA and snRNA levels gradually decreased over an eight year period in FFPE tissue blocks. Sample age was the most consistent feature associated with miRNA stability. The reference snRNA, RUN6B, was more rapidly degraded when compared to miR-141 and miR-221 miRNAs. Various miRNAs demonstrated differential rates of degradation. Quantitative miRNA studies from long-term archived FFPE tissues may therefore benefit from epidemiologic study design or statistical analysis methods that take into account differential storage-dependent transcript degradation.

A functional screen identifies miRNAs that inhibit DNA repair and sensitize prostate cancer cells to ionizing radiation.

MicroRNAs (miRNAs) have been implicated in DNA repair pathways through transcriptional responses to DNA damaging agents or through predicted miRNA regulation of DNA repair genes. We hypothesized that additional DNA damage regulating miRNAs could be identified by screening a library of 810 miRNA mimetics for the ability to alter cellular sensitivity to ionizing radiation (IR). A prostate cancer Metridia luciferase cell model was applied to examine the effects of individual miRNAs on IR sensitivity. A large percentage of miRNA mimetics were found to increase cellular sensitivity to IR, while a smaller percentage were protective. Two of the most potent IR sensitizing miRNAs, miR-890 and miR-744-3p, significantly delayed IR induced DNA damage repair. Both miRNAs inhibited the expression of multiple components of DNA damage response and DNA repair. miR-890 directly targeted MAD2L2, as well as WEE1 and XPC, where miR-744-3p directly targeted RAD23B. Knock-down of individual miR-890 targets by siRNA was not sufficient to ablate miR-890 radiosensitization, signifying that miR-890 functions by regulating multiple DNA repair genes. Intratumoral delivery of miR-890 mimetics prior to IR therapy significantly enhanced IR therapeutic efficacy. These results reveal novel miRNA regulation of DNA repair and identify miR-890 as a potent IR sensitizing agent.

Characterization of a novel metastatic prostate cancer cell line of LNCaP origin.

BACKGROUND: The LNCaP cell line was originally isolated from the lymph node of a patient with metastatic prostate cancer. Many cell lines have been derived from LNCaP by selective pressures to study different aspects of prostate cancer progression. When injected subcutaneously into male athymic nude mice, LNCaP and its derivatives rarely metastasize. METHODS: Here, we describe the characteristics of a new LNCaP derivative, JHU-LNCaP-SM, which was generated by long term passage in normal cell culture conditions. RESULTS: Short tandem repeat (STR) analysis and genomic sequencing verified JHU-LNCaP-SM derivation from parental LNCaP cells. JHU-LNCaP-SM cells express the same mutated androgen receptor (AR) but unlike LNCaP, are no longer androgen dependent for growth. The cells demonstrate an attenuated androgen responsiveness in transcriptional assays and retain androgen sensitive expression of PSA, AR, and PSMA. Unlike parental LNCaP, JHU-LNCaP-SM cells quickly form subcutaneous tumors in male athymic nude mice, reliably metastasize to the lymph nodes and display a striking intra-tumoral and spreading hemorrhagic phenotype as tumor xenografts. CONCLUSIONS: The JHU-LNCaP-SM cell line is a new isolate of LNCaP, which facilitates practical, preclinical studies of spontaneous metastasis of prostate cancer through lymphatic tissues.

Correlation of Sprouty1 and Jagged1 with aggressive prostate cancer cells with different sensitivities to androgen deprivation.

Prostate cancer is a heterogeneous disease and thus, it is important to understand whether among the heterogeneous collection of cell types, androgen-deprivation insensitive cells exist prior to hormonal manipulation. We established several LNCaP subclones with distinct insensitivities to androgen deprivation from a parental LNCaP cell line. In the resulting clones, the sensitivity to androgen-deprivation negatively correlated with their PSA expression levels. In two of these clones, an androgen insensitive clone, LNCaP-cl1, and an androgen sensitive clone, LNCaP-cl5, the DNA copy number differed significantly, indicating that these clones contain genetically distinct cells. LNCaP-cl1 had higher PSA expression but lower invasiveness and tumor growth potential than LNCaP-cl5. The expression levels of two genes that are known to be regulated by miR-21, an androgen-regulated microRNA, Sprouty1 (SPRY1) and Jagged1 (JAG1) were significantly lower in LNCaP-cl1 than in LNCaP-cl5. Knocking down SPRY1 in LNCaP cells enhanced PSA expression and cell proliferation. JAG1 administration in LNCaP cells enhanced cell invasion and JAG1 knockdown in PC3 cells suppressed cell invasion and tumor formation. These results indicated that the expression differences in SPRY1 and JAG1 may contribute to the phenotypic differences between the LNCaP-cl1 and LNCaP-cl5 clones. In tissue samples, SPRY1 expression levels were significantly lower in prostate cancer patients with PSA recurrence after surgical treatment (P = 0.0076) and JAG1 expression levels were significantly higher in Gleason sum (GS) 8-9 disease than in GS 5-6 (P = 0.0121). In summary a random population of LNCaP cells comprises a heterogeneous group of cells with different androgen-deprivation sensitivities and potential for invasiveness.

Investigation of miR-21, miR-141, and miR-221 expression levels in prostate adenocarcinoma for associated risk of recurrence after radical prostatectomy.

BACKGROUND: MicroRNAs (miRNAs) are small non-coding RNAs that regulate a broad array of cellular and disease processes. Several miRNAs are differentially expressed in cancer and many are being considered as biomarkers for predicting clinical outcomes. Here we quantified the expression of three miRNAs, miR-21, miR-141, and miR-221, from prostate cancer surgical specimens and evaluated their association with disease recurrence after primary therapy. METHODS: A pilot nested case-control study was designed from a large cohort of men who underwent radical prostatectomy between 1993 and 2001. Total RNA was extracted from malignant prostate tissue of 59 cases (recurrence) and 59 controls. Cases and controls were matched on age, race, pathologic stage, and grade. The relative expression of each miRNA was then determined for each sample by quantitative real-time RT-PCR. Conditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) of recurrence for tertiles of miRNA expression. We noted block storage time effects and thus, used separate tertile cutpoints based on the controls by calendar year of prostatectomy. RESULTS: Lower miR-221 expression was associated with a higher risk of recurrence; the ORs were 3.21 for the lowest tertile and 2.63 for the middle tertile compared with the highest tertile of expression (P-trend = 0.02). This pattern was unchanged after multivariable adjustment (P-trend = 0.05). No statistically significant trends were observed for miR-21 or miR-141 after multivariable adjustment. CONCLUSIONS: Based on this small pilot study, men with localized prostate cancers with lower miR-221 expression may have a greater risk for recurrence after surgery.

A novel approach for detecting viable and tissue-specific circulating tumor cells through an adenovirus-based reporter vector.

BACKGROUND: Circulating tumor cells (CTCs) hold great promise as biomarkers and are a direct source of tumor cells through a simple blood draw. However, CTCs are rare and their detection requires sensitive and specific methods to overcome the overwhelming hematocyte population. Therefore, CTC detection remains technically challenging. METHODS: An assay was developed for detecting viable and tissue-specific CTCs using a tropism-enhanced and conditionally replicating reporter adenovirus (CTC-RV). Adenoviral replication was made prostate-specific by placing the E1A gene under the control of the probasin promoter and prostate-specific antigen enhancer (PSE-PBN). Viral tropism was expanded through capsid-displayed integrin targeting peptides. A secreted reporter, humanized Metridia Luciferase (hMLuc), was engineered for expression during the major late phase of viral replication. The assay involves red blood cell lysis, cell collection, viral infection, and subsequent quantification of reporter activity from cellular media. Assay and reporter stability, cell specificity and sensitivity were evaluated in cell dilution models in human blood. RESULTS: A conditionally replicating prostate-selective adenovirus reporter and CTC assay system were generated. The secreted reporter, MLuc, was found to be stable for at least 3 days under assay conditions. CTC detection, modeled by cell dilution in blood, was selective for androgen receptor positive prostate cancer (PCa) cells. Serial dilution demonstrated assay linearity and sensitivity to as few as three cells. Prostate cancer cell viability declined after several hours in anticoagulated blood at ambient temperatures. CONCLUSIONS: Conditionally replicative adenoviral vectors and secreted reporters offer a functional method to detect viable CTCs with cell specificity and high sensitivity.

A novel source for miR-21 expression through the alternative polyadenylation of VMP1 gene transcripts.

miR-21 is the most commonly over-expressed microRNA (miRNA) in cancer and a proven oncogene. Hsa-miR-21 is located on chromosome 17q23.2, immediately downstream of the vacuole membrane protein-1 (VMP1) gene, also known as TMEM49. VMP1 transcripts initiate ∼ 130 kb upstream of miR-21, are spliced, and polyadenylated only a few hundred base pairs upstream of the miR-21 hairpin. On the other hand, primary miR-21 transcripts (pri-miR-21) originate within the last introns of VMP1, but bypass VMP1 polyadenylation signals to include the miR-21 hairpin. Here, we report that VMP1 transcripts can also bypass these polyadenylation signals to include miR-21, thus providing a novel and independently regulated source of miR-21, termed VMP1-miR-21. Northern blotting, gene-specific RT-PCR, RNA pull-down and DNA branching assays support that VMP1-miR-21 is expressed at significant levels in a number of cancer cell lines and that it is processed by the Microprocessor complex to produce mature miR-21. VMP1 and pri-miR-21 are induced by common stimuli, such as phorbol-12-myristate-13-acetate (PMA) and androgens, but show differential responses to some stimuli such as epigenetic modifying agents. Collectively, these results indicate that miR-21 is a unique miRNA capable of being regulated by alternative polyadenylation and two independent gene promoters.

Convergent alterations in the tumor microenvironment of MYC-driven human and murine prostate cancer.

The tissue microenvironment in prostate cancer is profoundly altered. While such alterations have been implicated in driving prostate cancer initiation and progression to aggressive disease, how prostate cancer cells and their precursors mediate those changes is unclear, in part due to the inability to longitudinally study the disease evolution in human tissues. To overcome this limitation, we performed extensive single-cell RNA-sequencing (scRNA-seq) and rigorous molecular pathology of the comparative biology between human prostate cancer and key time points in the disease evolution of a genetically engineered mouse model (GEMM) of prostate cancer. Our studies of human tissues, with validation in a large external data set, revealed that cancer cell-intrinsic activation of MYC signaling was the top up-regulated pathway in human cancers, representing a common denominator across the well-known molecular and pathological heterogeneity of human prostate cancer. Likewise, numerous non-malignant cell states in the tumor microenvironment (TME), including non-cancerous epithelial, immune, and fibroblast cell compartments, were conserved across individuals, raising the possibility that these cell types may be a sequelae of the convergent MYC activation in the cancer cells. To test this hypothesis, we employed a GEMM of prostate epithelial cell-specific MYC activation in two mouse strains. Cell communication network and pathway analyses suggested that MYC oncogene-expressing neoplastic cells, directly and indirectly, reprogrammed the TME during carcinogenesis, leading to the emergence of cascading cell state alterations in neighboring epithelial, immune, and fibroblast cell types that paralleled key findings in human prostate cancer. Importantly, among these changes, the progression from a precursor-enriched to invasive-cancer-enriched state was accompanied by a cell-intrinsic switch from pro-immunogenic to immunosuppressive transcriptional programs with coinciding enrichment of immunosuppressive myeloid and Treg cells in the immune microenvironment. These findings implicate activation of MYC signaling in reshaping convergent aspects of the TME of prostate cancer as a common denominator across the otherwise well-documented molecular heterogeneity of human prostate cancer.

Mechanism of growth inhibition of prostate cancer xenografts by valproic acid.

UNLABELLED: Valproic Acid (VPA), a histone deacetylase inhibitor, has been demonstrated to cause a marked decrease in proliferation of prostate cancer (PCa) cells in vitro and a significant reduction in tumor volume in vivo. The goal of this study is to better understand the VPA-induced growth inhibition in vivo, by studying expression of various markers in PCa xenografts. METHODS: For in vitro experiments, PCa cells were treated with 0, 0.6, and 1.2 mM VPA for 14 days. For in vivo models, experimental animals received 0.4% VPA in drinking water for 35 days. Tissue microarray was generated using cell pellets and excised xenografts. RESULTS: VPA treatment causes cell cycle arrest in PCa cells in vivo, as determined by increase in p21 and p27 and decrease in cyclin D1 expression. Increased expression of cytokeratin18 was also seen in xenografts. LNCaP xenografts in treated animals had reduced androgen receptor (AR) expression. While decreased proliferation was found in vitro, increase in apoptosis was found to be the reason for decreased tumor growth in vivo. Also, an anti-angiogenic effect was observed after VPA treatment. CONCLUSION: VPA inhibits tumor growth by multiple mechanisms including cell cycle arrest, induction of differentiation, and inhibition of growth of tumor vasculature.

Does valproic acid induce neuroendocrine differentiation in prostate cancer?

Valproic Acid (VPA) is a histone deacetylase inhibitor that holds promise for cancer therapy. Here, we investigate whether VPA treatment induces neuroendocrine differentiation of Prostate Cancer (PCa). A tissue microarray of VPA-treated and untreated tumor xenografts and cell lines of human PCa (LNCaP, C4-2, DU145, and PC-3) were generated and were analyzed by immunohistochemical analysis (IHC) for NE markers chromogranin A (CgA), synaptophysin, and NCAM (neural cell adhesion molecule). Western blot analysis for CgA was performed to confirm the results of the TMA. IHC analysis did not reveal any induction of CgA, synaptophysin, or NCAM in any xenograft after VPA treatment in vivo. In vitro, VPA treatment induced little synaptophysin expression in C4-2 and PC-3 cells and NCAM expression in LNCaP and PC-3 cells. In the case of CgA, VPA treatment decreased its expression in vitro in a dose-dependent manner, as determined by western blot analysis. Thus our data demonstrates that VPA does not induce NE differentiation of PCa cells in the physiologically relevant in vivo setting.

Alternative polyadenylation: An untapped source for prostate cancer biomarkers and therapeutic targets?

OBJECTIVE: To review alternative polyadenylation (APA) as a mechanism of gene regulation and consider potential roles for APA in prostate cancer (PCa) biology and treatment. METHODS: An extensive review of mRNA polyadenylation, APA, and PCa literature was performed. This review article introduces APA and its association with human disease, outlines the mechanisms and components of APA, reviews APA in cancer biology, and considers whether APA may contribute to PCa progression and/or produce novel biomarkers and therapeutic targets for PCa. RESULTS: Eukaryotic mRNA 3'-end cleavage and polyadenylation play a critical role in gene expression. Most human genes encode more than one polyadenylation signal, and produce more than one transcript isoform, through APA. Polyadenylation can occur throughout the gene body to generate transcripts with differing 3'-termini and coding sequence. Differences in 3'-untranslated regions length can modify post-transcriptional gene regulation by microRNAs and RNA binding proteins, and alter mRNA stability, translation efficiency, and subcellular localization. Distinctive APA patterns are associated with human diseases, tissue origins, and changes in cellular proliferation rate and differentiation state. APA events may therefore generate unique mRNA biomarkers or therapeutic targets in certain cancer types or phenotypic states. CONCLUSIONS: The full extent of cancer-associated and tissue-specific APA events have yet to be defined, and the mechanisms and functional consequences of APA in cancer remain incompletely understood. There is evidence that APA is active in PCa, and that it may be an untapped resource for PCa biomarkers or therapeutic targets.

A novel method for generating and screening peptides and libraries displayed on adenovirus fiber.

Capsid-displayed adenoviral peptide libraries have been a significant, yet unfeasible goal in biotechnology. Three barriers have made this difficult: the large size of the viral genome, the low efficiency of converting plasmid-based genomes into packaged adenovirus and the fact that library amplification is hampered by the ability of two (or more) virus to co-infect one cell. Here, we present a novel vector system, pFex, which is capable of overcoming all three barriers. With pFex, modified fiber genes are recombined into the natural genetic locus of adenovirus through unidirectional Cre-lox recombination. Modified-fiber genes can be directly shuttled into replicating viral genomes in mammalian cells. The 'acceptor' vector does not contain the fiber gene, and therefore does not propagate until it has received a 'donor' fiber gene. Therefore, This methodology overcomes the low efficiency of transfecting large viral genomes and bypasses the need for transition to functional virus. Thus, with a fiber-shuttle library, one can generate and evaluate large numbers of fiber-modified adenovirus simultaneously. Finally, successful fiber genes can be rescued from virus and recombined back into shuttle plasmids, avoiding the need to propagate mixed viral pools. For proof of principal, we use this new system to screen a capsid-displayed peptide library for retargeted viral infection.

PDCD4 Is an Androgen-Repressed Tumor Suppressor that Regulates Prostate Cancer Growth and Castration Resistance.

Androgen receptor (AR) transcriptional activity contributes to prostate cancer development and castration resistance. The growth and survival pathways driven by AR remain incompletely defined. Here, we found PDCD4 to be a new target of AR signaling and a potent regulator of prostate cancer cell growth, survival, and castration resistance. The 3' untranslated region of PDCD4 is directly targeted by the androgen-induced miRNA, miR-21. Androgen treatment suppressed PDCD4 expression in a dose responsive and miR-21-dependent manner. Correspondingly, AR inhibition dose-responsively induced PDCD4 expression. Using data from prostate cancer tissue samples in The Cancer Genome Atlas (TCGA), we found a significant and inverse correlation between miR-21 and PDCD4 mRNA and protein levels. Higher Gleason grade tumors exhibited significantly higher levels of miR-21 and significantly lower levels of PDCD4 mRNA and protein. PDCD4 knockdown enhanced androgen-dependent cell proliferation and cell-cycle progression, inhibited apoptosis, and was sufficient to drive androgen-independent growth. On the other hand, PDCD4 overexpression inhibited miR-21-mediated growth and androgen independence. The stable knockdown of PDCD4 in androgen-dependent prostate cancer cells enhanced subcutaneous tumor take rate in vivo, accelerated tumor growth, and was sufficient for castration-resistant tumor growth. IMPLICATIONS: This study provides the first evidence that PDCD4 is an androgen-suppressed protein capable of regulating prostate cancer cell proliferation, apoptosis, and castration resistance. These results uncover miR-21 and PDCD4-regulated pathways as potential new targets for castration-resistant prostate cancer.

Androgen receptor-modulatory microRNAs provide insight into therapy resistance and therapeutic targets in advanced prostate cancer.

Androgen receptor (AR) signalling is a key prostate cancer (PC) driver, even in advanced 'castrate-resistant' disease (CRPC). To systematically identify microRNAs (miRs) modulating AR activity in lethal disease, hormone-responsive and -resistant PC cells expressing a luciferase-based AR reporter were transfected with a miR inhibitor library; 78 inhibitors significantly altered AR activity. Upon validation, miR-346, miR-361-3p and miR-197 inhibitors markedly reduced AR transcriptional activity, mRNA and protein levels, increased apoptosis, reduced proliferation, repressed EMT, and inhibited PC migration and invasion, demonstrating additive effects with AR inhibition. Corresponding miRs increased AR activity through a novel and anti-dogmatic mechanism of direct association with AR 6.9 kb 3'UTR and transcript stabilisation. In addition, miR-346 and miR-361-3p modulation altered levels of constitutively active AR variants, and inhibited variant-driven PC cell proliferation, so may contribute to persistent AR signalling in CRPC in the absence of circulating androgens. Pathway analysis of AGO-PAR-CLIP-identified miR targets revealed roles in DNA replication and repair, cell cycle, signal transduction and immune function. Silencing these targets, including tumour suppressors ARHGDIA and TAGLN2, phenocopied miR effects, demonstrating physiological relevance. MiR-346 additionally upregulated the oncogene, YWHAZ, which correlated with grade, biochemical relapse and metastasis in patients. These AR-modulatory miRs and targets correlated with AR activity in patient biopsies, and were elevated in response to long-term enzalutamide treatment of patient-derived CRPC xenografts. In summary, we identified miRs that modulate AR activity in PC and CRPC, via novel mechanisms, and may represent novel PC therapeutic targets.

Aptamers and apple pies: a mini-review of PSMA aptamers and lessons from Donald S. Coffey.

This mini-review article is part of a special issue dedicated to Donald S. Coffey, a pioneer translational research scientist, exemplary mentor, and leader in urologic and urologic oncology research. This article first briefly reflects on life and scientific lessons from Don Coffey. It then reviews the development of two prostate cancer targeting RNA aptamers, xPSM-A9 and xPSM-A10, through in vitro selection for aptamers that bind to the extracellular domain of the Prostate Specific Membrane Antigen (PSMA). These 2'-fluorpyrimidine RNA aptamers selectively bind PSMA on the surface of prostate cancer cells, inhibit PSMA glutamate carboxypeptidase activity, and internalize into PSMA-expressing cancer cells. The truncation of both aptamers, through experimentation as well as logical design, has produced smaller isoforms including A10-3, A10-3.2, A9g and A9L. The larger aptamer isoforms xPSM-A9 and xPSM-A10 are limited to production by in vitro transcription and polyacrylamide gel purification, while smaller isoforms can be generated by chemically synthesis. A series of aptamer conjugates have been developed through chemical crosslinking, complementary annealing strategies, or a combination of both, for the targeting of experimental therapeutics to and into prostate cancer cells. The resulting aptamer conjugates, including nanoparticles and siRNA conjugates, selectively target PSMA-positive prostate cancer cells and xenograft tumors, and demonstrate potent cytotoxic and tumoricidal activity. These experimental therapeutic agents provide a platform for realizing and optimizing the potential of tumor-selective targeting and drug delivery.